linux-kernel - Re: [PATCH 4/7] usb: ehci-platform: add optional reset controller retrieval

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Message-ID: <Pine.LNX.4.44L0.1405081002190.1087-100000@iolanthe.rowland.org>
Date:	Thu, 8 May 2014 10:07:25 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Hans de Goede <hdegoede@...hat.com>
cc:	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Emilio Lopez <emilio@...pez.com.ar>,
	Mike Turquette <mturquette@...aro.org>, <kishon@...com>,
	Boris Brezillon <boris@...e-electrons.com>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-usb@...r.kernel.org>, <kevin.z.m.zh@...il.com>,
	<sunny@...winnertech.com>, <shuge@...winnertech.com>,
	<zhuzhenhua@...winnertech.com>, <linux-sunxi@...glegroups.com>,
	Boris BREZILLON <boris.brezillon@...e-electrons.com>
Subject: Re: [PATCH 4/7] usb: ehci-platform: add optional reset controller
 retrieval

On Thu, 8 May 2014, Hans de Goede wrote:

> Hi,
> 
> On 05/08/2014 12:00 AM, Maxime Ripard wrote:
> > On Wed, May 07, 2014 at 10:25:55AM -0400, Alan Stern wrote:
> >> On Tue, 6 May 2014, Maxime Ripard wrote:
> >>
> >>> From: Boris BREZILLON <boris.brezillon@...e-electrons.com>
> >>>
> >>> On the Allwinner's A31 SoC the reset line connected to the EHCI IP has to
> >>> be deasserted for the EHCI block to be usable.
> >>>
> >>> Add support for an optional reset controller that will be deasserted on
> >>> power off and asserted on power on.
> >>>
> >>> Signed-off-by: Boris BREZILLON <boris.brezillon@...e-electrons.com>
> >>> Signed-off-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
> >>
> >> Is this really a _reset_ line?  That is, when you assert the reset 
> >> line, does it actually reset the EHCI controller, or does it merely 
> >> leave the controller in a partially powered-down state?
> > 
> > It actually resets the whole controller.
> > 
> >> The difference is important.  During suspend, the controller is
> >> supposed to remember the state of the port connections as well as other
> >> settings.  If it doesn't, the controller and all attached USB devices
> >> will have to be reinitialized every time the controller resumes, which
> >> will increase the latency.
> > 
> > So you're saying that we should move this to the probe then?
> 
> Yes.

That's right.  The controller should not be reset during suspend, if
you can possibly avoid it.

There isn't any real benefit to asserting the reset signal during 
suspend, is there?  I mean, it won't use any less power, right?

Alan Stern

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